(1) Field of the Invention
The present invention relates to an improved return hole of a circulating path for rollers of a roller bearing for endless linear motion where a casing mounted on a track rail can make endless linear motion through a plurality of rollers circulating endlessly in said circulating path. The purpose of the present invention is to provide a return which is easy to manufacture, and which will produce various effects such as improved lubrication and cooling of the rollers, improved exhaust of foreign matters in the circulating path.
As shown in FIGS. 5 and 6, a roller bearing for endless linear motion consists of a track rail 1 of a linear shape and a casing 2 which mounts on said track rail 1, said casing 2 being able to make an endless linear motion through a plurality of rollers 3 circulating endlessly inside said casing 2. A circulating path for endlessly circulating said roller 3 comprises a load zone and a no load zone, said load zone consisting of a load track 6 formed by a right angle V groove 4 on said casing 2 and a right angle V groove 5 on said track rail 1, respectively opposing each other, said no load zone consisting of a return hole 7 of a linear shape formed in said casing 2 parallel to said load track 6, and a direction changing path 8 which smoothly changes the direction of said roller 3 by connecting respectively the both ends of said return hole 7 and said load track 6.
(2) Description of the Prior Art
In order to allow rolling of said roller 3 in said no load zone, in the prior art the return hole provided in the casing 2 is of a shape having a square cross section which is slightly larger than the cross section at the axis of the roller 3, said roller 3 being of a cylindrical shape, the height and diameter thereof being approximately same, and usually said return hole is provided in the casing 2. However, due to the positional relationship with the load track 6, the inclination of the square cross-sectioned return hole has to be made at a certain angle. Thus the process of producing such an inclined hole became difficult, and also the lubrication for the rollers rolling inside the return hole was not always performed smoothly. As a result, in order to improve the lubrication it was necessary to form separate oil holes.
Also as examples of other prior art, as shown in FIGS. 7 through 9, proposals were made to facilitate easy processing of the return hole. However, any one of these had defects as described in the following.
In the example shown in FIG. 7, casing 21 is divided into two portions, namely, upper portion 22 and lower portion 23, at a location of return hole 20. However, for a return hole 20, having a certain inclination, the division into two portions becomes difficult, and at the time of assembly of the upper portion 22 and the lower portion 23, assembly error or positional misalignment may occur between the upper portion 22 and the lower portion 23. Thus, a precisely shaped return hole 20 could not be obtained, and cases occurred in which the roller did not roll smoothly. As a result, there was a problem to use such a roller bearing for endless linear motion.
In the example shown in FIG. 8, return hole 24 is formed by fastening a return cover 30 made of a thin plate at the outside of casing 29. This is a relatively simple construction. However, although it is possible to adopt in a special case when return hole 24 is provided at the bottom surface of casing 29, in the case when the return hole is provided at a side surface or at a top surface of casing 29, the selection of the fastening area of the return cover 30 is difficult and cannot be adopted, and thus there is no universality.
In the example shown in FIG. 9, a return path of no load zone is formed by a right angle V groove 26 in casing 25, and an upper bearing plate 27 and a lower bearing plate 28, both of which bearing over the upper and lower outside surfaces of roller 3 respectively in a sliding and a contacting manner. Although the construction is very simple, since portions of the side surface and the end surface of roller 3 are exposed, depending upon the installation place of the roller bearing for endless linear motion, there is a large possibility of entrance of foreign matters into the return path, and thus there was a defect of a great risk existing to become unable to provide a stable guide.